The present invention relates to a communication system in a network having a plurality of interconnected local area networks, and more particularly to a local area network communication system suitable for communication between stations connected to different local area networks.
In a multi-ring network comprising a plurality of rings, an address of each station (ST) is represented by a ring number and a station number as defined in The Institute of Electrical and Electronics Engineers 802'5 Token Ring Draft. Each station must obtain an address of a destination station, that is, a station number and a ring number prior to communication.
Let us consider the movement of stations between a plurality of rings. It is important how each station obtains a destination ring number, because the address of the station changes whenever the station moves to another ring (reconnection) since the ring number changes.
In order to set the ring number of the destination station, the ring number of the destination may be preset in an initialization stage. In this method, whenever the station moves, the destination ring number must be obtained and reinitialization must be effected. When a station communicates with a station of unknown ring number, information may be sent to all of the plurality of rings in a manner of broadcasting communication. However, this method considerably increases the communication traffic.
A communication system between a plurality of rings is disclosed in "An Architecture for Interconnecting Token Rings" Kien-Bon K. Sy., Daniel Avery Pitt, By Contributions to IEEE 802.5 Feb. 13, 1984. This method also allows communication between stations of different rings. In this system, not the ring number of the destination station but path information to the destination station is to be obtained. The path information comprises number information of a series of repeating installations (which interconnect rings) leading to the destination station. Accordingly, the repeating installations have to be assigned their own installation numbers. In this sytem, a special path information storage area is provided in a communication frame. In this system, there is a problem that each station must be aware of its own ring number. The article is silent about how to obtain the ring number.
In a network having a plurality of interconnected local area networks (corresponding to rings), the same is applicable when the address used in the communication is represented by a local area network number and a station number.